The present invention relates a gas sensor having a sensor element capable of detecting the concentration of a specific gas component in gas under measurement and a manufacturing method of the gas sensor.
Hereinafter, the term “front” refers to a gas sensing side with respect to the axial direction of a gas sensor, and the term “rear” refers to a side opposite to the front side.
An exhaust gas sensor for an automotive vehicle is known, which includes, a sensor element, a lead wire, a metal shell and a protection cover. The sensor element has a gas sensing portion at a front end thereof to generate a detection signal responsive to the concentration of a specific gas component such as nitrogen oxide (NOx) or oxygen (O2) in exhaust gas and an electrode portion at a rear end thereof connected with the lead wire to output the detection signal from the gas sensing portion to an external device through the lead wire. The metal shell retains therein the sensor element with the gas sensing portion and the electrode portion protruding from front and rear ends of the metal shell, respectively. The protection cover is joined to the metal shell so as to cover and protect the electrical connection between the sensor electrode portion and the lead wire.
In general, the metal shell and the protection cover are joined together by laser welding. Japanese Laid-Open Patent Publication No. 2004-354274 and No. 2001-147213 disclose one such type of weld joint technique in which the metal shell and the protection cover are joined by fitting a front end portion of the protection cover around a rear end portion of the metal shell, optionally swaging the front end portion of the protection cover onto the rear end portion of the metal shell and irradiating a laser beam from the outside of the protection cover to form a laser weld joint between the front end portion of the protection cover and the rear end portion of the metal shell.